Revert "[ptr-traits] Implement the base pointer traits using the actual"

The commit we revert is rather small, but it enables a larger piece of new
infrastructure that allows to detected misuses of pointer-traits at compile
time. Unfortunately, this change breaks with the use of incomplete types (e.g.
in Polly). As I am not aware of a simple fix on the Polly side, I temporarely
revert this commit to clean the bots and sync-up with Chandler how to best
adapt to these recent changes.

This reverts commit https://llvm.org/svn/llvm-project/llvm/trunk@256620.

llvm-svn: 256642

llvm/include/llvm/Support/PointerLikeTypeTraits.h

@@ -15,7 +15,6 @@
 #ifndef LLVM_SUPPORT_POINTERLIKETYPETRAITS_H
 #define LLVM_SUPPORT_POINTERLIKETYPETRAITS_H
 
-#include "llvm/Support/AlignOf.h"
 #include "llvm/Support/DataTypes.h"
 
 namespace llvm {
@@ -28,32 +27,15 @@ template <typename T> class PointerLikeTypeTraits {
   // getNumLowBitsAvailable
 };
 
-namespace detail {
-/// A tiny meta function to compute the log2 of a compile time constant.
-template <size_t N>
-struct ConstantLog2
-    : std::integral_constant<size_t, ConstantLog2<N / 2>::value + 1> {};
-template <> struct ConstantLog2<1> : std::integral_constant<size_t, 0> {};
-}
-
 // Provide PointerLikeTypeTraits for non-cvr pointers.
-template <typename T> struct PointerLikeTypeTraits<T *> {
+template <typename T> class PointerLikeTypeTraits<T *> {
+public:
   static inline void *getAsVoidPointer(T *P) { return P; }
   static inline T *getFromVoidPointer(void *P) { return static_cast<T *>(P); }
 
-  enum {
-    NumLowBitsAvailable = detail::ConstantLog2<AlignOf<T>::Alignment>::value
-  };
-};
-
-template <> struct PointerLikeTypeTraits<void *> {
-  static inline void *getAsVoidPointer(void *P) { return P; }
-  static inline void *getFromVoidPointer(void *P) { return P; }
-
-  /// Note, we assume here that void* is related to raw malloc'ed memory and
-  /// that malloc returns objects at least 4-byte aligned. However, this may be
-  /// wrong, or pointers may be from something other than malloc. In this case,
-  /// you should specify a real typed pointer or avoid this template.
+  /// Note, we assume here that malloc returns objects at least 4-byte aligned.
+  /// However, this may be wrong, or pointers may be from something other than
+  /// malloc.  In this case, you should specialize this template to reduce this.
   ///
   /// All clients should use assertions to do a run-time check to ensure that
   /// this is actually true.